1. Field of the Invention
The present invention generally relates to a device capable of large conduction changes when locally compressed and decompressed. Specifically, the present invention is a sensor of sufficiently high sensitivity so as to enable pressure and stress measurements.
2. Description of the Related Art
Sensors are critical to the performance of keyboards, intrusion detection systems, and fluid control systems.
Musical keyboards employ carbon contacts to detect the depression of a key and a capacitive strip to measure how hard and fast the key is depressed so as to simulate the dynamic response of an instrument. Keys are susceptible to dirt, moisture, and other contaminants. Mechanical solutions adversely effect pressure detection and penalize the dynamic range of the instrument.
Intrusion systems include optical and laser devices for detection purposes. Devices are difficult to conceal and readily defeatable. Furthermore, such systems are limited in their mapping capability and therefore do not provide a complete record of an intrusion, including, but not limited to, location and time, to resolve direction of travel and speed.
Fluid control systems for cooling, fire suppression, and fuel transport require inline sensors to accurately measure pressure for the active control of valves and pumps. However, such systems must function within a harsh environment including rapidly changing pressures. Diaphragm-based gages offer reliable pressure measurement, even when surrounded by corrosive and high temperature fluids, but are generally too bulky for inline use. Furthermore, low sensitivity and high cost limit the application of diaphragm-based devices to all but the most critical systems.
High-sensitivity pressure sensors are sorely needed for the above referenced applications, as well as for other applications, including submarines, torpedoes, sonobuoys, industrial and commercial keyboards, doors, and switches. Composites having one or more pressure variable properties are critical to a new class of sensors for use within the applications above.
Polymer-metal composites having variable resistance are described in U.S. Pat. No. 4,028,276. Compositions experience an actual change in electric properties, namely, resistance, when compressed by a mechanical load. Practical applications of these materials require a complete and uniform compression of the composite cross its presented area. As such, a large force is required for proper function. Resultantly, polymer-metal composites lack the fidelity necessary to accurately measure pressure and stress and thereby limited to sensing gross magnitudes and differentials.
Pressure conduction composites exhibit a change in conductance in response to a mechanical load. Unlike polymer-metal composites, pressure conduction composites do not experience an actual resistance change. Rather, compression alters the spatial arrangement of conductive particles within a non-conductive matrix as so to enable a change in conduction between particles about the critical percolation threshold of the material system. Small localized mechanical loads or pressures cause a very large change in the “effective” resistance at the output of the composite. This highly localized sensitivity greatly improves the signal-to-noise ratio and usable signal strength from the composite. Furthermore, pressure conduction composites are inherently resistant to the deleterious effects of dirt, moisture, and other contaminants.
Therefore, what is currently required is a high-sensitivity sensor including a pressure conduction composite capable of detecting and measuring pressure and/or stress.
Furthermore, what is currently required is a high-sensitivity sensor including a pressure conduction composite that is sufficiently robust to avoid the deleterious effects of harsh environments.
Furthermore, what is currently required is a high-sensitivity sensor including a pressure conduction composite having a compact, conformal form of minimal volume.
Furthermore, what is currently required is a high-sensitivity sensor including a pressure conduction composite that is easily configurable to enable a matrix arrangement for large spatial applications.